I bought a J3 a couple of weeks ago, and have yet to update my firmware. The J3 came with 2.03 installed. It seems to work fine (no album art or playlist issues here ;-p), but I'd like to try 2.22 out. However, if I'm not happy with it, I'd like to be able to get back to where I am now.

I've searched for a downloadable version of the 2.03 firmware, but had no luck. Is it possible to back up the firmware from my player? Do I just need to copy some of the system folders and then copy them back if I want to revert to 2.03 or is it more involved than that?

They only thing you will ever back up will be your settings.
All the user settings are located in the j3 folders. The Sytem folder to be exact.
Copy that folder to your desktop and have it sit there if you lose your settings and dont want to mess around having to re-do them again. Perfect if you use the BBE and Jet Effect.

the firmware is added on your j3 and you can not back it up.
You can, however, download the new or old firmware from the website so you can downgrade and upgrade as much as needed.

They only thing you will ever back up will be your settings.
All the user settings are located in the j3 folders. The Sytem folder to be exact.

I think even more specifically it's the PARAM.CFG file (in the \System folder) which represents your settings and configuration. It's probably just that file which is crucial.

Certainly if you delete that file and re-boot you'll now be back to "factory defaults" for everything and will need to re-customize. This is functionally equivalent to "RESET", or more extremely if you FORMAT the J3 (to FAT32).

Note that FORMAT (the most extreme "RESET") will erase everything on the J3. And then the first re-boot after that will trigger the currently installed firmware to re-build all of the default folder structures, populated with whatever may be default file contents (also obtained from firmware).

Obviously your \Music and \Video folders will be empty, and you'll need to create your own \Playlist folder if you want one (since that doesn't seem to be rebuilt automatically).

The \System\MusicDB folder (which holds the resized 95x95 mini-versions of all of your full-sized album art JPGs used by Matrix Browser, named as AB_nnn.jpg and created at boot time by the [check albums] function) is likewise initially empty. But as you add music/art folders/files, each reboot will trigger [check albums] and the \MusicDB folder will be automatically maintained.

Nothing else which may actually have been on your J3 initially (e.g. \Windows98 on mine, for whatever purpose) is apparently critical (at least for operation of the J3 with WinXP and Win7). So losing them with FORMAT appears harmless.